Influence of benthic macroinvertebrates on mixing of profundal sediments in southeastern Lake Huron

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110017/1/lno19782351011.pd

Radioactivity in sediments of the Great Lakes: Post-depositional redistribution by deposit-feeding organisms

At two locations in southern Lake Huron (U.S.A.), twelve 35.5-cm diameter cores of fine-grained sediments were taken for comparison of the vertical distributions of 210Pb and falllout 137Cs with the distributions of benthic macroinvertebrates, mainly oligochaete worms (Tubificidae) and the amphipod, Pontoporeia affinis. Locations were selected on the basis of 210Pb distributions measured a year earlier which indicated contrasting depths of mixing of surface sediments. At one location the activity of 210Pb is uniform down to about 6 cm and 95% of total invertebrates occur within this zone; at the other location the zone of constant activity is only 3 cm deep but 90% of the invertebrates occur within it. Comparison of published tubificid defecation rates with sediment accumulation rates based on 210Pb shows that oligochaetes alone can account for mixing in one case while the effects of amphipods may be required in the case of shallower mixing. If mixing is represented as a diffusional process, eddy diffusion coefficients are at least 5.8 and 3.3 cm2 yr-1 at respective locations. In comparison with bioturbation, molecular diffusion is of minor importance in the post-depositional mobility of 137Cs. The necessity for introducing a diffusion coefficient varying continuously with depth is indicated by characteristics of the distribution of 137Cs. Biological reworking of near-surface sediments is an important process affecting radioactivity and chemical profiles in profundal deposits of this and probably other Great Lakes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22852/1/0000413.pd

Effect of deposit feeders on migration of 137Cs in lake sediments

Illite clay particles with adsorbed 137Cs were added as a submillimeter layer to the surface of silt-clay sediments contained in rectangular Plexiglas cells stored in a temperature-regulated aquarium, in order to trace the effect of the oligochaete, Tubifex tubifex, and the amphipod, Pontoporeia hoyi, on mass redistribution near the sediment-water interface. A well-collimated NaI gamma detector scanned each sediment column (~10 cm deep) at daily or weekly intervals for six months, depicting the time evolution of radioactivity with and without added benthos. In a cell with tubificids (~5 x 104 m-2), which feed below 3 cm and defecate on surface sediments, the labeled layer was buried at a rate of 0.052 +/- 0.007 cm/day (20[deg]C). When labeled particles entered the feeding zone, 137Cs reappeared in surface sediments creating a bimodal activity profile. In time, the activity tended toward a uniform distribution over the upper 6 cm, decreasing exponentially below to undetectable levels by 9 cm. In a cell with amphipods (~1.6 x 104 m-2) uniform activity developed rapidly (~17 days) down to a well-defined depth (1.5 cm). The mixing of sediments by Pontoporeia is described by a simple quantitative model of eddy diffusive mixing of sediment solids. The value of the diffusion coefficient, 4.4 cm2/yr (7[deg]C) was computed from a least squares fit of theoretical to observed profile broadening over time. In a cell without benthos, small but measurable migration of 137Cs indicated an effective molecular diffusion coefficient of 0.02 cm2/yr.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23642/1/0000606.pd

A study of the primary productivity of the phytoplankton of Lancaster Lake, Cheboygan County, Michigan.

http://deepblue.lib.umich.edu/bitstream/2027.42/52827/1/1260.pdfDescription of 1260.pdf : Access restricted to on-site users at the U-M Biological Station

Isotope ratios of H, C, and O in CO2 and H2O of the Martian atmosphere

Stable isotope ratios of H, C, and O are powerful indicators of a wide variety of planetary geophysical processes, and for Mars they reveal the record of loss of its atmosphere and subsequent interactions with its surface such as carbonate formation. We report in situ measurements of the isotopic ratios of D/H and O-18/O-16 in water and C-13/C-12, O-18/O-16, O-17/O-16, and (CO)-C-13-O-18/(CO)-C-12-O-16 in carbon dioxide, made in the martian atmosphere at Gale Crater from the Curiosity rover using the Sample Analysis at Mars (SAM)'s tunable laser spectrometer (TLS). Comparison between our measurements in the modern atmosphere and those of martian meteorites such as ALH 84001 implies that the martian reservoirs of CO2 and H2O were largely established similar to 4 billion years ago, but that atmospheric loss or surface interaction may be still ongoing